The Tolo Channel Geo-Area includes the north shore of Tolo Channel, Ma Shi Chau on the southwest shore and Lai Chi Chong on the south shore. Most of the rocks along the north shore of Tolo Channel and at Bluff Head are the oldest in Hong Kong, formed about 400 million years ago during the Devonian Period. Ma Shi Chau presents the sedimentary rocks formed about 280 million years ago; the rocks are the second oldest rocks in the rock region; Lai Chi Chong showcases various volcanic rocks and sedimentary rocks formed about 146 million years ago. These two geo-sites also show distinctive geological features, such as faults and folds. Although the geology of Ma Shi Chau and Lai Chi Chong is a bit complicated, they are the ideal destinations for geologists.
The 61-hectare Ma Shi Chau is made up of Ma Shi Chau, Yeung Chau, Centre Island and an unnamed islet to the northeast of Sam Mun Tsai New Village. Ma Shi Chau is the key site of Hong Kong's Permian Tolo Harbour Formation. Home to well-outcropped rocks, the island is an ideal location for studying strata, rock properties, sedimentation features and different geological compositions because here you can find faults and folds as well as deformed and displaced rock mass. The unnamed islet near Yim Tin Tsai, vegetated with dense woodlands, is a popular roosting ground for egrets and herons. Given such outstanding conservation value, the Ma Shi Chau region was declared a protected Special Area in 1999.
The Ma Shi Chau nature trail runs along the southeastern shore of the island. 1.5 km in length, this route presents 16 attractions which highlight local geological features. By observing the rocks on site and reading trailside interpretation plates, visitors can understand how tombolos and various rocks are formed, as well as natural phenomena like wave erosion, weathering and folding .